Within a computer network having a number of network nodes, a system time is generally defined such that the clock associated with each node can be brought into agreement with, i.e., synchronized, with the system time. For example, a computer network may include a plurality of computer devices networked together with each computer device defining a respective node. As such, a common system time can be provided to each of the computing devices such that the clock of each computing device can be synchronized to the system time. By establishing a common system time within a computer network, communication can be facilitated. For example, data collected by one of the network nodes and provided to other ones of the network nodes can be appropriately correlated and/or fused with other data as a result of the common system time. In this regard, the time at which data is collected by two or more nodes of a computer network will be defined in terms of a common system time and can therefore be appropriately analyzed or otherwise processed in accordance with the common timeframe.
In order to maintain a common system time for each of the plurality of nodes within a computer network, a master clock sync signal is typically broadcast on a periodic basis to all of the network nodes. Upon receipt, the network nodes then set their respective local clocks to be equal to the system clock.
While the use of a master clock sync signal has proven to be generally workable for a relatively fixed computer network having a predefined network architecture and a predetermined number of network nodes, the use of a master clock sync signal has proven to be less advantageous for mobile ad hoc networks. In this regard, mobile ad hoc networks are formed of a collection of network nodes which are permitted to join and leave the mobile ad hoc network in a random manner over time. As such, the mobile ad hoc network does not have a predefined network configuration, but is, instead, continually evolving as various network nodes join and/or leave the mobile ad hoc network. Mobile ad hoc networks generally permit some or all of the network nodes to be mobile and therefore typically rely upon wireless communications between the network nodes, thereby creating the need for network nodes to join the mobile ad hoc network in a random manner as new network nodes become positioned so as to be in communication with the mobile ad hoc network and to leave the mobile ad hoc network in a random manner as the network nodes become positioned in such a manner as to lose communication with the mobile ad hoc network.
The number and variety of mobile ad hoc networks are increasing. By way of one example, a mobile ad hoc network may be comprised of the portable computing devices, such as personal digital assistants (PDAs), mobile telephones, laptop or other portable computers, or the like, carried by a group of people who are in the same vicinity, such as within a meeting room or other venue. As such, the individuals could communicate with one another via their respective computing devices with computing devices joining and leaving the mobile ad hoc network on a random basis as individuals carrying the respective computing devices enter and exit, respectively, the venue. As another example, the computing devices onboard each vehicle positioned at a predefined locale, such as the computing devices onboard each tank or other military vehicle positioned within a particular region, may comprise a network node of a mobile ad hoc network. As such, the computing devices carried by one vehicle could communicate with the computing devices carried by another vehicle via the mobile ad hoc network. As before, network nodes may join or leave the mobile ad hoc network as vehicles carrying computing devices arrive at the locale or exit the locale, respectively.
While the use of a master clock sync signal to set the system time has been workable for fixed network configurations, the disadvantages of a master clock sync signal are accentuated in the context of a mobile ad hoc network in which network nodes are permitted to join and leave the network on a random basis. As a result of network nodes joining an existing mobile ad hoc network at different times, the need to initially establish the system time for a new network node prior to its joinder to the mobile ad hoc network occurs more frequently. Since a master clock sync signal is generally only broadcast periodically to the network nodes, including the nodes that have newly joined the network, it sometimes occurs that a node that has recently joined a mobile ad hoc network must refrain from sending information across the mobile ad hoc network until after the node has received the periodically broadcast master clock sync signal. In instances in which it is desirable for a new node to join a mobile ad hoc network and commence communications with other nodes of the mobile ad hoc network, such a delay in communications with the new node of the mobile ad hoc network can be disadvantageous.
Reliance upon a master clock sync also has other disadvantages. For example, the periodic broadcast of the master clock sync signal disadvantageously adds to the communications burden that must be supported by the mobile ad hoc network. Also, as a result of the flexibility provided by a mobile ad hoc network with respect to the random joinder and exit of nodes to and from the mobile ad hoc network, a mobile ad hoc network that periodically broadcasts a master clock sync signal may experience the departure of the node that has provided the master clock sync signal. In this instance, nodes that thereafter join the mobile ad hoc network will not receive a master clock sync signal and will therefore be out of time synchronization with respect to the other network nodes of the mobile ad hoc network.
Accordingly, it would be desirable to provide an improved technique for establishing a common system time for the network nodes of a mobile ad hoc network. In this regard, it would be desirable to provide an improved technique for defining a common system time for a mobile ad hoc network that permits network nodes to join in a random manner and communicate across the network without delay, but with notice of the common system time.